My invention relates to electric amplifiers in general and, in particular, to a differential amplifier system for providing an output proportional to the difference between the voltages applied to its two inputs. More particularly, my invention concerns such a differential amplifier system of the class particularly well suited for use in the deflection circuits of oscilloscopes, among other applications.
A typical conventional differential amplifier system (shown in FIG. 1 of the drawings attached hereto) has been of such construction that the output current magnitude varies nonlinearly with the inputs, resulting in output distorsion. The output has also been subject to distortion or drift, particularly when the input is of low frequencies, due to changes in the base emitter junction temperatures of the transistors in use.
I am aware of a more advanced differential amplifier system (FIG. 2) free from such drawbacks of the more conventional one. However, the collector to base voltages of the transistors used in this second prior art system fluctuates considerably in a low frequency range. Therefore, if a high frequency signal being amplified has zero or low frequency components superimposed thereon, the frequency characteristic is subject to change with the magnitude of the superimposed signal components. Further the second prior art system has had problems in amplifying as wide a range of frequencies as can be desired. I will later describe the problems attendant on the noted conventional systems in further detail.